System and method for production of silicon using horizontal magnetic field

Abstract

To provide a system for producing a silicon ingot by the horizontal magnetic field Czochralski method.SOLUTION: A system for producing a silicon ingot includes: a natural sand crucible containing a silicon melt in which a cristobalite layer having a thickness between 0.25 mm and 1.25 mm is formed on an inner wall of the crucible; magnetic poles for generating a horizontal magnetic field; and a controller programed to produce a silicon ingot according to the following steps: rotating the natural sand crucible containing a silicon melt at two to five revolutions per minute; applying a horizontal magnetic field to the crucible using the magnetic poles; contacting the silicon melt with a seed crystal; and withdrawing the seed crystal from the silicon melt while rotating the natural sand crucible at two to five revolutions per minute to form a silicon ingot.SELECTED DRAWING: Figure 4

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 62 / 947,785, filed December 13, 2019, the entire disclosure of which is incorporated herein by reference. [Technical Field]

[0002] The present disclosure relates generally to the production of silicon ingots, and more particularly to methods and systems for achieving a high success rate in producing silicon ingots in the Czochralski process using a horizontal magnetic field. [Background technology]

[0003] During the 1990s, at least some high-quality silicon growth was primarily controlled by the thermal conditions of the puller, particularly the hot zone (HZ) design, since the ratio of pull rate to thermal gradient (v / G) was considered the dominant factor. In the late 1990s, at least some high-quality silicon growth incorporated further consideration of the crystal / melt interface at the same v / G. Around this time, as more customers transitioned from epi to polish and from 200mm to 300mm, the application of high-quality silicon to memory devices began to expand in earnest. Soon after, it was established that high-quality silicon growth required highly stable process growth conditions and controlled melt flow to achieve the specific crystal / melt ratios necessary to achieve the desired low crystal defect rate during growth.

[0004] Peripherally, as silicon crystal growth moved from 200 mm to 300 mm and the corresponding increase in charge size to maintain productivity, the need for magnetic field application to stabilize melt flow in the increased melt volume became recognized as a dominant feature.

[0005] Some silicon manufacturers transitioned to the horizontal magnetic field Czochralski process (HMCZ) in the early 2000s when high-quality 300mm silicon production began to take place in order to effectively control the crystal / melt interface. Other silicon manufacturers used cusp magnetic fields for high-quality 300mm silicon production. In either case, the magnetic field in the silicon melt dramatically affects the quality and performance of the crystal, and all manufacturers developed their own techniques to optimize performance and quality from the start.

[0006] During the CZ process and magnetic field-assisted single-crystal silicon ingot production, oxygen can be introduced into the silicon crystal ingot through the melt-solid interface or the melt-crystal interface. This oxygen can cause various defects in the wafers produced from the ingot and reduce the yield of semiconductor devices manufactured using the ingot. For example, low interstitial oxygen concentration (Oi) is generally required to achieve high resistivity in applications such as memory devices, insulated-gate bipolar transistors (IGBTs), high-quality radio frequency (RF), high-resistivity silicon-on-insulator (HR-SOI), and charge-trapped SOI (CTL-SOI). The HMCZ process generally required a very low crucible rotation (C / R) to control the oxygen content in the growing crystal, particularly within the desired range applicable to memory devices. Furthermore, it was found that the incidence of crown-to-body-edge zero-loss dislocations (LZDs) was higher in the HMCZ process compared to processes using a cusp magnetic field.

[0007] Thus, there is a need for a method and system that reduces LZD loss in HMCZ growth and provides improved ZD success rates for high quality silicon growth from crown to body.

[0008] This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and / or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. Summary of the Invention

[0009] In one aspect of the present disclosure, a method for producing a silicon ingot by a horizontal magnetic field Czochralski process includes rotating a crucible containing a silicon melt, applying a horizontal magnetic field to the crucible, contacting the silicon melt with a seed crystal, and withdrawing the seed crystal from the silicon melt while rotating the crucible to form a silicon ingot. The crucible has a wettable surface on which a cristobalite layer is formed.

[0010] Another aspect is a wafer produced from a silicon ingot manufactured using the method described above.

[0011] Another aspect is a system for producing a silicon ingot, the system including a controller configured to produce the silicon ingot according to the method described above.

[0012] Various refinements exist to the features noted in connection with the above-described aspects. Additionally, additional features may be incorporated into the above-described aspects as well. These enhanced and additional features may exist individually or in any combination. For example, various features described below in connection with any of the illustrated embodiments may be incorporated into the above-described aspects alone or in any combination. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a top view of a crucible according to one embodiment. [Figure 2] FIG. 2 is a side view of the crucible shown in FIG. [Figure 3] 1 is a schematic diagram illustrating a horizontal magnetic field applied to a crucible containing a melt in a crystal growth apparatus. [Figure 4] FIG. 1 is a block diagram of a crystal growth system. [Figure 5] The temperature field (mm) of the free surface of the melt and the rotation speed (RPM) of the crucible by MGP are shown. [Figure 6] 1 is a graph of crystallization rate as a function of time. [Figure 7] 1 is a graph showing the thickness of the layer formed as a function of time at a temperature of 1360° C. [Figure 8] 1 is a contour plot of ZD success rate and amount of melt modifier by crucible rotation in a natural sand crucible.

[0014] Like reference symbols in the various drawings indicate like elements. DETAILED DESCRIPTION OF THE INVENTION

[0015] 1 and 2, one embodiment of a crucible is generally designated 10. The cylindrical coordinate system of crucible 10 includes a radial direction R 12, an angular direction θ 14, and an axial direction Z 16. Crucible 10 contains a melt 25 having a melt surface 36. A crystal 27 grows from melt 25. Melt 25 may include one or more convection cells 17, 18 caused by heating crucible 10 and rotation of crucible 10 and / or crystal 27 about the angular direction θ 14. As described in more detail below, the structure and interaction of these one or more convection currents 17, 18 are controlled via adjustment of one or more process parameters and / or application of a magnetic field.

[0016] FIG. 3 illustrates a horizontal magnetic field applied to a crucible 10 containing a melt 25 in a crystal growing apparatus. As shown, the crucible 10 contains a silicon melt 25 from which a crystal 27 is grown. The transition between the melt and the crystal is commonly referred to as the crystal-melt interface (alternatively, the melt-crystal, solid-melt, or melt-solid interface) and is typically nonlinear, e.g., concave, convex, or gull-wing shaped relative to the melt surface. Two magnetic poles 29 are positioned opposite each other to generate a magnetic field generally perpendicular to the crystal growth direction and generally parallel to the melt surface 36. The magnetic poles 29 may be conventional electromagnets, superconducting electromagnets, or any other suitable magnet for generating a horizontal magnetic field of the desired strength. The application of the horizontal magnetic field generates a Lorentz force along the axial direction, opposite the fluid motion, counteracting the force driving the melt convection. This suppresses melt convection and increases the axial temperature gradient of the crystal near the interface. The melt-crystal interface then moves upward toward the crystal in accordance with the increasing axial temperature gradient of the crystal near the interface, reducing the contribution of melt convection within the crucible. The horizontal configuration has the advantage of being more efficient at damping convection at the melt surface 36.

[0017] FIG. 4 is a block diagram of a crystal growth system 100. The system 100 employs the Czochralski crystal growth method to produce semiconductor ingots. In this embodiment, the system 100 is configured to produce cylindrical semiconductor ingots having an ingot diameter of one hundred fifty millimeters (150 mm), a diameter greater than one hundred fifty millimeters (150 mm), more specifically in the range of about 150 mm to 460 mm, and even more specifically about three hundred millimeters (300 mm). In other embodiments, the system 100 is configured to produce semiconductor ingots having an ingot diameter of two hundred millimeters (200 mm) or an ingot diameter of four hundred millimeters (450 mm). Additionally, in one embodiment, the system 100 is configured to produce semiconductor ingots having a total ingot length of at least nine hundred millimeters (900 mm). In some embodiments, the system is configured to produce semiconductor ingots having lengths of one nineteen hundred millimeters (1950 mm), two two hundred fifty millimeters (2250 mm), two three hundred fifty millimeters (2350 mm), or greater than 2350 mm. In other embodiments, the system 100 is configured to produce semiconductor ingots having total ingot lengths ranging from about nine hundred millimeters (900 mm) to one twelve hundred millimeters (1200 mm), between about nine hundred millimeters (900 mm) and about two thousand millimeters (2000 mm), or between about nine hundred millimeters (900 mm) and about two five hundred millimeters (2500 mm). In some embodiments, the system is configured to produce semiconductor ingots having total ingot lengths greater than 2000 mm.

[0018] Crystal growth system 100 includes a vacuum chamber 101 that surrounds crucible 10. A side heater 105, e.g., a resistance heater, surrounds crucible 10. A bottom heater 106, e.g., a resistance heater, is positioned below crucible 10. During heating and crystal pulling, a crucible drive unit 107 (e.g., a motor) rotates crucible 10, e.g., clockwise, as indicated by arrow 108. Crucible drive unit 107 may also raise and / or lower crucible 10 as desired during the growth process. Within crucible 10 is silicon melt 25 having melt level or melt surface 36. In operation, system 100 pulls a single crystal 27 from melt 25, starting from a seed crystal 115 attached to a pulling shaft or cable 117. One end of the lifting shaft or cable 117 is connected via a pulley (not shown) to a drum (not shown) or any other suitable type of lifting mechanism, e.g., a shaft, and the other end is connected to a chuck (not shown) that holds the seed crystal 115 and the crystal 27 grown from the seed crystal 115.

[0019] The crucible 10 and the single crystal 27 share a common axis of symmetry 38. The crucible drive unit 107 can raise the crucible 10 along axis 38 as the melt 25 is depleted to maintain the melt level 36 at a desired height. The crystal drive unit 121 similarly rotates the pulling shaft or cable 117 in a direction 110 opposite to the direction in which the crucible drive unit 107 rotates the crucible 10 (e.g., counter-rotation). In embodiments using equal rotation, the quartz crystal drive unit 121 may rotate the pulling shaft or cable 117 in the same direction (e.g., clockwise) as the crucible drive unit 107 rotates the crucible 10. Equal rotation is also referred to as co-rotation. Additionally, the crystal drive unit 121 raises and lowers the crystal 27 relative to the melt level 36 as desired during the growth process.

[0020] According to the Czochralski single crystal growth process, a predetermined amount of polycrystalline silicon, or polysilicon, is loaded into crucible 10. Heater power supply 123 energizes resistive heaters 105, 106, and insulation 125 lines the interior walls of vacuum chamber 101. Gas supply 127 (e.g., a bottle) supplies argon gas to vacuum chamber 101 via gas flow controller 129 as vacuum pump 131 removes the gas from vacuum chamber 101. An outer chamber 133, supplied with cooling water from reservoir 135, surrounds vacuum chamber 101.

[0021] The cooling water then drains to a cooling water return manifold 137. Typically, a temperature sensor, such as a photoelement 139 (or pyrometer), measures the temperature at the surface of the melt 25, and a diameter transducer 141 measures the diameter of the single crystal 27. In this embodiment, the system 100 does not include a top heater. The presence, or absence, of a top heater changes the cooling characteristics of the crystal 27.

[0022] Magnetic pole 29 is positioned outside vacuum chamber 101 to generate a horizontal magnetic field (shown in FIG. 3). Although shown approximately centered above melt surface 36, the position of magnetic pole 29 relative to melt surface 36 may be varied to adjust the position of the maximum Gauss plane (MGP) relative to melt surface 36. A reservoir 153 supplies cooling water to magnetic pole 29 before draining via cooling water return manifold 137. An iron shield 155 surrounds magnetic pole 29 to reduce stray magnetic fields and enhance the strength of the generated magnetic field.

[0023] The control unit 143 is used to adjust multiple process parameters, including, but not limited to, at least one of the crystal rotation speed, the crucible rotation speed, and the magnetic field strength. In various embodiments, the control unit 143 may control a memory 173 and a processor 144 that process signals received from various sensors of the system 100, including, but not limited to, the optical element 139 and the diameter transducer 141, as well as one or more devices of the system 100, including, but not limited to, the crucible drive unit 107, the crystal drive unit 121, the heater power supply 123, the vacuum pump 131, the gas flow controller 129 (e.g., an argon flow controller), the magnetic pole power supply 149, and any combination thereof. The memory 173 may store instructions that, when executed by the processor 144, cause the processor to perform one or more of the methods described herein. That is, the instructions configure the control unit 143 to perform one or more of the methods, processes, procedures, etc. described herein.

[0024] The control unit 143 may be a computer system. As described herein, a computer system refers to any known computer device and computer system. As described herein, all such computer systems include a processor and a memory. However, any processor in a computer system referred to herein can also refer to one or more processors, whether the processor is in a single computer device or in multiple computer devices operating in parallel. Furthermore, any memory in a computer device referred to herein can also refer to one or more memories, whether the memory is in a single computer device or in multiple computer devices operating in parallel. Furthermore, the computer system may be located near the system 100 (e.g., in the same room or an adjacent room) or may be located remotely and connected to the rest of the system via a network such as Ethernet, the Internet, etc.

[0025] As used herein, the term processor refers to a central processing unit, microprocessor, microcontroller, reduced instruction set circuit (RISC), application specific integrated circuit (ASIC), logic circuit, and any other circuit or processor capable of performing the functions described herein. These are examples only and are therefore not intended to limit in any way the definition and / or meaning of the term "processor." Memory may include, but is not limited to, random access memory (RAM), such as dynamic RAM (DRAM) or static RAM (SRAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and non-volatile RAM (NVRAM).

[0026] In one embodiment, a computer program is provided for implementing the control unit 143, the program being embodied on a computer-readable medium. The computer-readable medium may include the memory 173 of the control unit 143. In an exemplary embodiment, the computer system is implemented on a single computer system. Alternatively, the computer system may comprise multiple computer systems, a connection to a server computer, a cloud computing environment, or the like. In some embodiments, the computer system includes multiple components distributed among multiple computing devices. One or more components may be in the form of computer-executable instructions embodied on a computer-readable medium.

[0027] The computer system and processes are not limited to the specific embodiments described herein. Furthermore, each computer system component and each process can be implemented independently and separately from other components and processes described herein. Each component and process can also be used in combination with other assembly packages and processes.

[0028] In one embodiment, the computer system may be configured to receive measurements from one or more sensors, including, but not limited to, temperature sensor 139, diameter transducer 141, and any combination thereof, or to control one or more devices of system 100, such as, but not limited to, crucible drive unit 107, crystal drive unit 121, heater power supply 123, vacuum pump 131, gas flow controller 129 (e.g., argon flow controller), pole power supply 149, and any combination thereof, as described herein and shown in Figure 4. The computer system performs all steps used to control one or more devices of system 100, as described herein.

[0029] The loss of zero-dislocation (ZD) structure (quantified by the LZD rate) is generally higher during silicon crystal Cz growth in a horizontal magnetic (HMCZ) field than during growth in a cusp (or vertical) magnetic field. However, the LZD rate in HMCZ dramatically decreases when crystals are grown in synthetic sand crucibles rather than natural sand crucibles. However, while the ZD rate improves, the cost of synthetic liner crucibles is higher than that of natural sand crucibles. Furthermore, thin (approximately 2 mm thick) synthetic liners melt within a relatively short process time, exposing the backing sand layer to the melt, potentially allowing quartz particles to penetrate the melt and impinge on the growing crystal. This increases the risk of air bubbles within the liner or from the backing sand to the melt. To avoid backing sand contamination due to air bubble exposure and / or melting when using synthetic liner crucibles, the process high-temperature time is generally limited to less than ~250 hours, a much shorter process time than can be achieved with natural sand crucibles (approximately 400–500 hours or more). Because high-temperature time for crystal growth depends on process conditions, HZ configuration, and runs, using a synthetic liner crucible can impact refill capacity and the growth of multiple rods per batch. Therefore, silicon growth using HMCZ in a synthetic liner crucible generally requires optimization of crucible conditions to ensure the highest ZD rate and minimum runs so that maximum refill capacity can be achieved.

[0030] Furthermore, the horizontal magnets used in Cz growth promote melt flow by continuously striking the crucible wall with strong force, creating irregular melt waves with transient behavior. In this case, the surface condition of the crucible is crucial for the production of quartz flakes, which are directly related to the success of ZD. As shown in Figure 5, the melt flow and temperature field are significantly affected by the strength of the magnetic field and the position of the MGP. As shown in the figure, the circumferential temperature variation at the melt surface changes significantly depending on the magnetic field direction.

[0031] These and other difficulties can be overcome or alleviated in embodiments of the present disclosure by using one or both of two techniques, described in detail below. Generally, in a first aspect, a cristobalite layer is formed on a wettable surface inside the crucible. The wettable surface generally refers to the surface of the crucible that may come into contact with the melt during silicon production. The wettable surface generally includes the interior bottom of the crucible, at least a portion of the interior sidewall of the crucible, and the interior portion connecting the interior sidewall and bottom of the crucible. In FIG. 2, the wettable surface is all of the interior surface of the crucible 10 below and including the melt surface 36. The wettable surface may also extend above the melt surface 36. A second technique described in this disclosure is increasing the rotation speed of the crucible.

[0032] Generally, a strong, unsteady melt flow is induced by the HMCZ magnetic field, which can generate strong thermomechanical stresses and mechanical shocks on the crucible wall, causing quartz grain generation. However, a high crucible rotation rate (C / R) generates faster convection near the crucible wall, which can disrupt the magnetically driven melt flow. This reduces the stress and shock on the wall. As a result, quartz grain generation on the wall is reduced, which in turn reduces LZD during crystal growth.

[0033] LZD can also be reduced by the formation of a generally uniform crystalline SiO2 layer (called the cristobalite layer) on the wettable surface of the crucible. This layer is more stable and stronger than amorphous quartz itself, and therefore more resistant to melt attack by stress or mechanical shock. The cristobalite layer therefore reduces the generation of quartz particles.

[0034] There are at least two methods for promoting crystal layer growth on a quartz crucible. One is to use a crucible pre-coated with a compound such as BaOH that promotes cristobalite growth. The other is to add a suitable melt modifier (MM) to the melt before crystal growth. Non-limiting examples of suitable MMs include barium (Ba) and strontium (Sr). More specifically, non-limiting examples of suitable MMs include barium carbonate (BaCO), barium oxide (BaO), and strontium carbonate (SrCO).

[0035] Cristobalite formation on the inner wall of amorphous quartz is governed by factors such as pressure, Oi concentration, HO and hydrogen content, and temperature. As shown in Figures 6 and 7, the formation and growth of the crystalline layer on the crucible wall is governed by the crucible wall temperature and the concentration of MM consumed in the crucible. Figure 6 compares the crystallization rate as a function of time for no MM and 8% Al2O3 MM. Figure 7 compares the layer thickness formed at 1360 °C as a function of time for no MM, 8% Al2O3 MM, and barium-based MM. These graphs demonstrate that adding an appropriate MM (e.g., barium-based MM) to the melt or pre-coating with a barium compound can produce a uniform, thick crystalline (i.e., cristobalite) layer on the wall of a natural sand crucible, resulting in behavior and performance similar to that of a synthetic liner crucible. Because the cristobalite layer dissolves more slowly than fused quartz, it is less susceptible to quartz fragmentation due to thermal and mechanical stress, suppressing the subsequent formation of crystalline LZD. Furthermore, the occurrence of secondary bubbles in the BFL (Bubble Free Layer) of a natural sand crucible and their propagation into the melt are generally much less than in a synthetic sand crucible due to differences in material properties.

[0036] The formation and growth of a uniform cristobalite layer, either through pre-coating of the crucible or post-addition of a melt modifier to the melt, is initiated during the stabilization mode (i.e., after or during melting of the polysilicon) prior to crystal growth. In the case of post-addition of MM, the cristobalite formation rate is slower than in the case of non-pre-coating because MM is introduced after melting. However, post-addition of MM reduces air pocket (APK) loss by allowing trapped air bubbles formed on the crucible wall to escape to the surface before the stable cristobalite layer forms. Since it typically takes 3 to 7 hours from the start of the stabilization step to the onset of main growth, the thickness of the cristobalite is estimated to be approximately 2 mm or more when an appropriate amount of MM is added to enhance the cristobalite formation rate. In practice, a cristobalite layer of approximately 1.0 mm or less typically forms on the surface of a crucible (whether made of natural or synthetic sand). ++ and N ++In special cases, such as the heavily doped process described above, thicker cristobalite layers can be obtained by adding larger amounts of MM. In such cases, cristobalite layers of approximately 1.0 mm (±) are formed. These thicknesses differ from 2.0 mm because the cristobalite layer grows over the hot time, while the wet cristobalite layer is continuously dissolved in the melt, as shown in FIG. 7. Other embodiments include cristobalite layers formed on the wettable surface of the crucible that are approximately 2.0 mm, greater than 1.5 mm, greater than 1.0 mm, greater than 0.75 mm, greater than 0.5 mm, or greater than 0.25 mm. In some embodiments, the cristobalite layer is less than 3.0 mm thick, less than 2.0 mm thick, less than 1.25 mm thick, or less than 1.0 mm thick. In some embodiments, the cristobalite layer falls within the range defined by the minimum and maximum values ​​described above, such as between 0.25 mm and 1.25 mm. Generally, a cristobalite layer that is too thin may be insufficient to provide the benefits described herein, while a cristobalite layer that is too thick may be more likely to break off and enter the melt (which may contribute to LZD) during silicon production.

[0037] The addition of the melt modifiers described above forms a uniform crystalline layer on the wettable surface of the crucible, and this crystalline structure is highly resistant to the thermomechanical stresses caused by the irregular (transient) melt flow that occurs during HMCZ. The formation of a thick, uniform cristobalite layer can resist the stresses and impacts from the melt flow, reducing damage to the crucible surface (i.e., resisting damage that would cause quartz particles in the melt) and increasing the success of ZD.

[0038] As mentioned above, the strong convection caused by the high rotation of the crucible suppresses temperature fluctuations at the free surface of the melt and reduces the melt flow caused by the horizontal magnet, as seen in Case 6 in Figure 5. The C / R is 0.6 RPM in Cases 1 to 5 and Case 7, while it is 1.6 RPM in Case 6. This indicates that the force generated by the magnetic field from the melt to the crucible wall is reduced or inhibited by the convection caused by the high rotation of the crucible. This reduces the possibility of quartz chips being generated due to damage to the crucible wall and improves the chances of successful ZD.

[0039] Test conditions were conducted to understand the ZD success rate of synthetic liner crucibles and natural sand crucibles in a horizontal magnetic field as a function of crucible rotation speed and melt modifier addition. The synthetic crucibles demonstrated high ZD success rates over a wide range of crucible rotations and mm. For the natural sand liner crucible, a total of 96 trials were conducted at 19 different conditions, and the results are summarized in the contour plots in Figure 8. The data in Figure 8 are from approximately 200 mm of body length to near the OE of the crystal. In Figure 8, CR is the crucible rotation speed (RPM), a %Success_3 of 0.0 indicates ZD failure (LZD), and a %Success_3 of 1.0 indicates 100% ZD success. The sign of the crucible rotation indicates the direction of crucible rotation. In some pulls, the crucible rotation ramped between speeds during portions of the pull, and arbitrary values ​​of crucible rotation were selected for plotting. Data were collected from over 1000 mm of body length to approximately the OE of the crystal. The results clearly show that increasing the absolute value of the crucible rotation speed and the amount of melt modifier (in this case Ba-based) achieves a higher ZD success rate.

[0040] Increasing the crucible rotation speed and using cristobalite layer formation, both individually and in combination, have been shown to result in improved ZD results. At low C / Rs, such as between about 0 and about 2 RPM, the addition of appropriate MM (or the use of a precoated crucible) is necessary to increase the ZD success rate. As the C / R increases from about 2 RPM to about 5 RPM, the amount of MM required to achieve the same success rate decreases, and MM may even be zero. Within this range, the use of at least MM can further improve ZD success rates. Above about 5 RPM, ZD from the crucible is generally not a concern, and MM is likely unnecessary. However, at such speeds, additional process conditions are likely required to control product quality, as there may be other issues, such as oxygen control via melt flow rate and melt level control via centrifugal force.

[0041] Therefore, some embodiments of the present disclosure use more than 1.7 grams of MM per square meter of crucible wettable surface during the HMCZ process at a given C / R rate to improve ZD success rates. In some embodiments, 1.7 to 2.0 grams / m of crucible wettable surface is used. 2 In yet another embodiment, 1.7 to 5.4 grams / m 2 of the wettable surface of the crucible is used. 2 In yet another embodiment, a MM of between 5.4 grams / m 2 of the wettable surface of the crucible is used. 2 Larger MM may be used, but large amounts of MM may cause LZD during multiple refill processes. 2 ) is when BaCO3 is used as the MM. Similar embodiments using BaO or SrCO3 include an amount of the specified MM that is functionally equivalent to the amount of BaCO3.

[0042] Some embodiments are from about 0 to 0.5 g / m 2 In some such embodiments, the crucible is a natural sand crucible. Alternatively, the crucible may be a synthetic crucible.

[0043] Embodiments of the methods described herein achieve superior results compared to previous methods and systems. For example, the methods described herein facilitate producing silicon with a higher ZD success rate than some other methods.

[0044] When introducing elements of the invention or embodiments thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the element. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0045] Approximate language used throughout this specification and claims may be applied to modify any quantitative expression that can be permissibly varied without resulting in a change in the basic function to which it relates. Thus, values ​​modified by terms such as "about," "approximately," and "substantially" are not limited to the exact value specified. In at least some instances, approximating language may correspond to the precision of an instrument for measuring the value. Throughout this specification and claims, range limitations may be combined and / or interchangeable, and such ranges identify and include all subranges contained therein, unless the context or language indicates otherwise.

[0046] Since various changes as noted above can be made without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted in an illustrative and not a limiting sense.

Claims

1. 1. A method for producing a silicon ingot by a horizontal magnetic field Czochralski process, comprising: rotating a crucible containing a silicon melt and having a wettable surface with a cristobalite layer formed thereon; applying a horizontal magnetic field to the crucible; contacting a silicon melt with a seed crystal; and pulling a seed crystal from the silicon melt while rotating the crucible to form a silicon ingot.

2. The method of claim 1 , wherein the crucible comprises a natural sand crucible.

3. adding solid phase polycrystalline silicon to a natural sand crucible; and 3. The method of claim 2, further comprising the step of heating the polycrystalline silicon to form a silicon melt.

4. 4. The method of claim 3, further comprising adding a melt modifier to the natural sand crucible to form a cristobalite layer on the wettable surface of the natural sand crucible.

5. 5. The method of claim 4, wherein the step of adding a melt modifier comprises adding the melt modifier and heating the polycrystalline silicon to form a silicon melt.

6. 5. The method of claim 4, wherein adding the melt modifier comprises adding the melt modifier after the silicon melt is formed.

7. The step of adding a melt modifier is performed by adding barium carbonate (BaCO ３ The method according to any one of claims 4 to 6, comprising the step of adding

8. 8. The method of claim 7, wherein the step of adding barium carbonate includes adding at least 1.7 grams per square meter of wettable surface of the natural sand crucible.

9. The step of adding a melt modifier may include adding barium oxide (BaO) or strontium carbonate (SrCO ３ 7. The method according to claim 4, further comprising the step of adding any one of the following:

10. 10. The method of claim 9, wherein the step of adding one of barium oxide or strontium carbonate comprises adding one of barium oxide or strontium carbonate in an amount substantially equivalent to 1.7 grams of barium carbonate per square meter of wettable surface of the natural sand crucible.

11. 4. The method of claim 3, wherein the step of adding the solid phase polycrystalline silicon to the natural sand crucible comprises the step of adding the solid phase polycrystalline silicon to a natural sand crucible having a barium-based coating already formed on a wettable surface of the natural sand crucible.

12. The method according to any one of claims 1 to 11, wherein the step of rotating the natural sand crucible includes a step of rotating the natural sand crucible at least two revolutions per minute.

13. The method of any one of claims 1 to 12, wherein the cristobalite layer has a thickness of about 2.00 mm or more.

14. A wafer produced from a silicon ingot by the method according to any one of claims 1 to 13.

15. A controller configured to produce a silicon ingot according to the method of any one of claims 1 to 13. A system for producing silicon ingots.

Images